Here is a simple recipe for rehydration salts to use as treatment for dehydration from heat exposure or diarrhea:
8 tsp. Sugar
1 tsp. Salt
1 liter of drinkable water

1 tsp. is about equal to one level bottle cap. If honey is available, it can be used in the place of the sugar. Do not use honey for children under 3 yrs. old.
If oranges or orange juice is available, mix the honey or sugar in 1 cup of orange juice. Mix the salt into a separate cup of water. Add 1 tsp. of baking soda to the salt water. Alternate sips of the orange juice and the salt water. Then, follow this down with another 2 cups of water.
These drinks should not be kept overnight